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Remote sensing for resources development and environmental management
Damen, M. C. J.

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rectangular box filter across the image. The
advantage of such a process is to produce a more
consistent image. However, since the filter cannot
discriminate between small scene variations and
systematic and random noise, both tend to be removed
or reduced in amplitude.
For applications where there is an interest in the
detection of subtle linear features, (for example the
identification of subterranean field drains), it has
been found useful to perform a variable filter edge
enhancement, the filter size being dependant on the
particular feature of interest. The most commonly
used filters range from 3 X 3 to 15 X 15 pixels in
dimension. Once the feature of interest has been
enhanced by this process it has also been found
useful to apply a median filter; this resamples the
data in a 3 X 3 box. By using this process isolated
pixels caused by the edge enhancement procedure tend
to be removed.
A further processing operation is required if the
project requires quantitative absolute temperature
values. In order to obtain such information
calibration of the imagery needs to be carried out
using ground temperature measurements obtained at the
time of the aircraft overpass. Correlation of these
ground measurements with the unstretched digital
numbers can be used to establish the limits for a
quantitative density slice representing discrete
temperature levels. The application of this technique
to heat loss monitoring is presented in section 6.
As mentioned previously several flights of the Barr
and Stroud IR18 TVFS were performed during August
1984 as part of a preliminary research assessment of
the instrument. As a consequence of early morning
mist these flights took place from late morning until
late afternoon rather than, as planned, during the
post-sunset/ pre-dawn period. The imagery obtained
was, nevertheless, useful since it enabled the
potential of the imagery to be assessed together with
methods of processing the imagery (Dele, 1985)
More recently both the Barr end Stroud and RPC
TVFS systems have been flown, for a variety of
projects by ERSAC Ltd. The following material
reports some of the most significant applications to
6.1 Heat Loss Monitoring.
Several projects have been carried out using the Barr
and Stroud IR18 to assess heat loss from industrial
and residential buildings. As mentioned above, in
order to provide quantitative estimates of localised
heat loss from TVFS imagery it is necessary to
establish calibration data to relate the grey scale
variations on the image to emitted radiance and
eventually to estimates of heat emission. In addition
to deriving emitted temperature it is also necessary
to evaluate the variations in emissivity over the
Ground temperature measurements can be obtained
using either conventional in-situ temperature probes
(e.g. thermistors or thermometers) or alternatively
by using ground based radiometric measurements from
instruments such as the AGA Thermovision. As
mentioned earlier the AGA Thermovision is a low
spatial resolution system; however, it is possible,
by using a blackbody reference, to obtain ground
temperature measurements. By using the Stefan-
Boltzmann law the heat loss for a particular
temperature value can be derived and a suitable
density slice for the IR18 imagery obtained. The
results of one particular set of date are shown in
Table 4.
If the computed heat losses (Q) from Table 4 are
regressed on the mean digital number indicating
emitted radiance (R) from the IR18, then a regression
coeffiecient (r) of 0.924 is obtained. The
Table 4. Calibration of Heat Loss from Barr and
Stroud IR18 using data from the AGA Thermovision
Mean Computed
Heat Loss (Q)
coefficient of determination (r 2 ) is 0.854,
indicating that 85% of the computed heat losses from
the calibration results above can be explained by the
corresponding radiance values (R) as recorded and
digitised from the IR18 sensor data. The resulting
heat loss regression equation for the IR18, for the
8°c gain setting was of the form;
Q = 0.4185R - 12.537 ....(1)
with a standard error of ±6 watts.
6.2 Thermal Mapping of Roads
A novel environmental engineering application of the
IR18 TVFS system has involved thermal mapping of road
surfaces in winter to identify accident black spots.
The primary objective of this night-time aerial
survey work was to assist road engineers in the
siting of ground sensors to monitor ice conditions
around high accident risk sections of road. It is
also hoped that the data will enable improvements and
ecomomies in road gritting operations to be achieved.
The survey was carried out in Scotland in February
1986. Ground temperature measurements were obtained
and used to determine calibration data for the IR18.
By using this data in conjunction with the GEMS image
processing system it was possible to digitise and
calibrate a selected number of frames of data. Using
a digital to analogue converter it was then possible
to create from these selected scenes, a density
sliced video image of the original analogue tape.
This feature has been shown to be of considerable
benefit to non specialists viewing the imagery.
6.3 Geotechnical Site Investigations
An assessment of the potential of the IR18 to detect
solution features in chalk will be carried out during
the summer of 1986. Solution features are a serious
geotechnical hazard and generally provide unreliable
bearing capacity for foundations. A review of the
significance of solution features end the use of
remote sensing techniques for their detection is
provided in Kennie and Edmonds (1986). The relative
performance of TVFS and thermal infrared linescanning
techniques will also be investigated during this
6.4 Drainage, Sewer Collapse and Utilities Surveys
A recent application of the IR18 has involved the
detection of subsurface utilities and problems
associated with such features. In this case the TVFS
was mounted on a boom attached to a car and was used
in conjunction with a ground impulse radar system
(x = 6 to 330 centimetres).